test_runner: remove runtime experimental warning

This commit removes the experimental warning that is emitted
when the test runner is used. The test runner feature is still
considered experimental, but this change makes its output
easier to read.

PR-URL: nodejs#44844
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/test.js

@@ -2,9 +2,6 @@
 const { ObjectAssign } = primordials;
 const { test, describe, it, before, after, beforeEach, afterEach } = require('internal/test_runner/harness');
 const { run } = require('internal/test_runner/runner');
-const { emitExperimentalWarning } = require('internal/util');
-
-emitExperimentalWarning('The test runner');
 
 module.exports = test;
 ObjectAssign(module.exports, {